Redshift might block when no network connectivity is available (if it
tries to determine the location automatically). To avoid this blocking
the whole status line, immediately release the lock in the query thread.
Move updating of redshift information into a separate thread so that
errors like missing network connectivity do not block the whole status
bar.
fixes#61
In order to do that, change the theme engine so that a theme can
override settings in the iconsets. Was probably a bug to begin with that
this was not possible.
